67 twin turbo dart

You must be way soft on timing to be able to run even 5lbs on 87 octane. Seems like a recipe for disaster honestly. I’d hate to see you hurt that motor for a couple bucks/gallon. I’ve run 87 in a pinch or on drag week stuff for long drives but we really pull the tune back and stay out of the throttle.
I'll get a picture of the timing table, have only messed a tiny bit with it.